A former British colony, Hong Kong was returned to China in 1997. But due to the "one country, two systems" formula, Beijing agreed to give the region a great deal of autonomy and to preserve its economic and social systems for 50 years.

Why is this important for China?

China is extremely - and increasingly - sensitive about what it says are questions of national sovereignty.

Beijing's main focus is Hong Kong and the self-ruling island of Taiwan. In Taiwan's case, China's position is straightforward: Beijing sees Taiwan as a breakaway province that rightfully belongs to the mainland.